The development of arterial constrictions, or stenoses, due to atherosclerotic plaques, or other causes, is a common occurrence in the circulatory system. Although in most instances the reason for the initial development of the stenosis is unknown it is clear that once a constriction is present it provides a disturbance to the normal blood flow through the artery, with potentially serious medical implications. The objective of the project is to determine the pertinent hydrodynamic characteristics related to flow in arterial stenoses, and to ascertain the role of these characteristics in the development of arterial disease associated with the presence of stenotic obstructions. By means of both in vitro and in vivo tests the following characteristics, and their interrelationships, are to be investigated: (1) stenosis geometry, (2) flow resistance, (3) turbulence created by the stenosis, and (4) turbulence induced effects such as wall vibrations and flow induced sounds. The in vitro tests will be performed using models having well- defined geometries and operated under various types of flow conditions, both steady and unsteady. The in vivo tests will be performed by introducing artificial stenoses into the carotid arteries, abdominal aortas, and coranary arteries of large mongrel dogs and obtaining similar measurements to those obtained in the in vitro tests.